(a) Field of the Invention
The present invention relates to a liquid crystal display and a driving method thereof.
(b) Description of Related Art
A liquid crystal display (LCD) is one of the most prevalent flat panel displays, which includes two panels having a plurality of electrodes for generating electric field, a liquid crystal (LC) layer interposed therebetween, and two polarization films attached to outer surfaces of the two panels. The LCD varies voltages applied to the field-generating electrodes to re-orient LC molecules in the LC layer, which determine polarization of light passing through the LC layer. The polarization films changes transmittance of the light based on the variation of the light polarization. Therefore, desired images are obtained by controlling the voltages applied to the field-generating electrodes. One of the panels includes thin film transistors (TFTs) for switching the voltages applied to the field-generating electrodes.
In the center of the panel on which the TFTs are formed, a display area on which an intended image is displayed is placed. In the display area, a plurality of signal lines, that is, a plurality of gate lines and data lines are formed in row and column directions, respectively. In a pixel area, which is defined by the crossing of the gate line and data line, a pixel electrode is formed, and the TFT controls the data signal transmitted via the data line according to the gate signal transmitted via the gate line to provide it to the pixel electrode.
A plurality of gate pads and data pads, which are connected to the gate lines and data lines, respectively, are formed outside the display area, and those pads are connected to external driving ICs to receive the gate signals and data signals from the outside and transmit them to the gate lines and data lines.
To transmit the gate signal and data signal, a gate printed circuit board (“PCB”) and a data PCB are attached to the TFT panel through a thermal press process using an anisotropic conducting film (“ACF”). Connected between the TFT panel and the data PCB is a flexible printed circuit (“FPC”) for data signal transmission on which a data driving IC that transforms an electric signal to a data signal and outputs it to the data pad and data line is mounted. Also, connected between the TFT panel and the data PCB is an FPC for gate signal transmission on which a gate driving IC that transforms an electric signal to a gate signal and outputs it to the gate pad and gate line is mounted.
The structure that the data driving IC and gate driving IC are connected to the TFT panel and PCB via transmission film has disadvantages that additional mounting space are required between the TFT panel and PCB for placing the IC to the transmission film to make the overall size larger and that contact defect may be generated due to the attachment of the IC to the transmission film.
To solve the above problems, a chip on class (“COG”) structure in which the data IC and/or gate IC is mounted directly on the TFT panel and the IC and the PCB are connected using the transmission film is used.
However, in case that at least two data ICs are mounted on the TFT panel in the COG type LCD, since a plurality of transmission films, on which data wiring for transmitting signal data, control data, and gray data received from the signal controller of the PCB are formed, are arranged in parallel, it causes disadvantages that manufacturing cost increases due to the use of many expensive transmission films and that mounting space for connecting the transmission film to each data IC is required.
In addition, the large number of the connections between data ICs and transmission films causes disadvantages of high cost and high contact defect rate.
A cascade structure, in which a data signal is provided by connecting a transmission film to one side and the signal provided from one side is provided to each data IC arranged in parallel by a shift operation of the data IC, is suggested to resolve the above disadvantages.
However, in the conventional LCD having such a cascade structure or another, a data controller circuit of the PCB transmits data to the data driving IC using RSDS (Reduced Swing Differential Signal) or conventional TTL method. For example, in case that 6-bit data are transmitted, since R, G, and B data with clock signal should be transmitted separately in TTL level transmission method, total nineteen (19) signal lines (clock signal line (1)+respective signal lines (6*3)=19) are required.
In addition, in case of RSDS transmission method, since the signals of positive and negative polarities for each signal are transmitted simultaneously, total twenty (20) signal lines (clock signal line (2)+respective signal lines (9*2)=20) are required.
As described above, even though a cascade structure is used, still there is a disadvantage that the number of the signal lines increase, and therefore, the possibility of noise increase becomes higher due to the influences between signal lines.